n  i   I '  ' 


U.  S.  DEPAR  IMI'A  r  OF  AGRICULTURE 

BUREAU  OF  PL  \N  I  INDUSTRY     Circular  No 
K.   l    GALLOW  v>    I  in.  I  ol  Bui 


MUTATIVE  REVERSIONS  IN  COTTON. 


O.   I-.  COOK. 


•-10 — 1 


.ton  :  Govt"...  .  orncc  :  i»u 


*T^Jk^ 


BUREAU  OF  PLANT  INDUSTRY. 


Chief  of  Bureau,  Beverly  T.  Gallows  r. 

Assistant  Chit]  of  Bur  tan .  ('..  Harold  1'owell. 
Editor,  J.  E.  Rockwell. 
Chuf  Clerk,  James  E.  Tones. 
[(  ir.53] 
2 


II  p  I 


MUTATIVE  REVERSIONS  IX  COTTON. 


INTRODUCTION. 

It  is  customary  hr  writers  on  heredity  and  breeding  to  look  upon 
reversions  and  mutations  as  rare  and  exceptional  phenomena,  but 
mutative  variations  of  the  cotton  plant  are  of  frequent  occurrence 
ami  many  of  them  appear  to  I)'-  reversions.  Knowledge  of  the  nature, 
extent,  and  causes  of  such  reversions  would  throw  light  upon  many 
problems  of  breeding  and  adaptation  <>f  varieties,  for  variations  <>f 
this  kind  appear  to  be  onr  of  tin*  chief  factum  of  deterioration. 

Many  pronounced  variations  occur  in  cotton  as  sequels  of  hybrid- 
isation and  among  the  diversities  aroused  by  new  conditions.  Indi- 
vidual variations  seldom  appear  to  differ  from  the  parent  stock  by  a 
single  feature,  l>ut  usually  show  numerous  peculiar  characteristics 
outside  of  the  ordinary  range  of  variation  of  the  parental  types. 
The  cotton  plant  affords  an  unusually  favorable  opportunity  for  the 

observation   of  such    facts   because  SO   many  of  its   parts  are    readily 
seen  and  compared. 

Changes  of  characters  are  not  confined  to  stocks  thai  have  been 
recently  hybridized.  Even  in  the  most  uniform  varieties,  such  as 
the  Triumph  Upland  cotton  of  Texas,  many  individual  plants  ma\ 
show  sudden  departures  from  the  normal  characters  of  the  variety, 
especially  when  the  conditions  are  new  or  extreme.  The  nature  of 
such  variations  and  the  frequency  with  which  they  occur  indicate 
that  they  represent  reversions  to  the  earlier  diversities  of  the  type  thai 
have  been  suppressed  by  selection." 

Reversion  may  he  defined  as  the  return  of  ancestral  characters  to 
expression.  Plants  or  animals  that  differ  from  their  immediate  rela- 
tives in  showing  characteristics  .>f  remote  ancestors  are  described 

isions,  or  "throw-backs."  Striped  pigs,  black  lambs,  blue 
pigeons,  red  ears  of  corn,  and  brown-linted  cotton  plants  that  appeal 
occasionally  in  pure-bred  white  varieties  may  he  looked  upon 
reversions  to  the  characteristics  of  colored  ancestors.  Reversions 
may  he  reckoned  as  partial  if  the  variant  individuals  bring  into 
expression  only  a  few  of  the  ancestral  peculiarities  ami  in  other 
respects  continue  to  resemble  the  typical  members  of  the*  breed. 

il  Adjustment  of  Cotton  Varieties.     Bulletin  159,  Bureau  of  Plant  Industry, 
-    Dept.  of  Agriculture,  1909,  j- 

iClr.  531 


4  MUTATIVE   REVERSIONS   IN    COTTON. 

Reversions  may  be  called  total  or  complete  when  there  are  changes 
of  whole  series  of  characters  of  parent  varieties.  ♦ 

REVERSIONS  SIMILAR  TO  MUTATIONS. 

Whether  wild  species  originate  by  sudden  mutative  variations  or 
not,  there  can  be  no  doubt  in  the  case  of  the  cotton  plant  that  definite 
variations  occur  and  that  they  can  give  rise  to  new  cultivated  varieties. 
The  great  majority  of  such  variations  are  not  preserved  because  they 
are  inferior  to  existing  types.  In  a  uniform,  big-boiled  type  of  cotton, 
such  as  the  Triumph,  many  small-boiled  individuals  with  different 
habits  of  growth  and  other  peculiarities  may  suddenly  appear.0 

In  dilute  hybrid  stocks  of  Egyptian  cotton,  with  only  a  small  pro- 
portion of  Upland  or  Hindi  blood,  individual  plants  of  apparently 
"pure"  Upland  or  Hindi  cotton  are  found,  while  the  other  plants  of 
the  same  ancestry  show  only  the  usual  Egyptian  characters.  If  the 
Egyptian  parentage  of  these  variations  were  not  known  it  would  not 
be  suspected  from  any  of  the  characters  that  are  brought  into  expres- 
sion. If  the  experiments  had  been  conducted  on  a  smaller  scale 
and  only  the  Upland  or  the  Egyptian  type  had  been  familiar,  these 
changes  of  characters  might  have  been  looked  upon  as  rare  muta- 
tions into  new  species,  like  those  that  occur  in  the  garden  variety  of 
the  evening  primrose  studied  by  Professor  De  Vries  in  Holland. 

It  does  not  seem  probable  that  the  mutative  changes  of  characters 
that  often  occur  in  cultivated  stocks  of  cotton  represent  the  attain- 
ment of  new  characters,  for  the  characters  that  come  into  expression 
in  this  way  are  commonly  found  among  the  more  primitive  types  of 
cotton.  Even  the  characters  that  have  received  the  largest  amount 
of  selective  "improvement"  from  breeders,  such  as  large  bolls  and 
long,  strong  lint,  have  been  found  to  exist  in  equal  or  greater  degree 
in  related  types  of  cotton  that  have  been  cultivated  only  in  tropical 
America  without  any  conscious  methodical  selection  by  the  Indians. 

The  more  degenerate  variations  of  the  Upland  cotton,  with  very 
small  bolls  and  very  short  lint,  are  inferior  to  any  of  the  varieties 
cultivated  in  the  United  States,  so  that  they  can  not  be  looked  upon 
as  results  of  crossing  with  other  varieties,  except  as  crossing  may 
be  supposed  to  induce  reversions.  It  is  not  necessary  to  suppose 
that  these  inferior  characters  are  new,  for  some  of  them  are  closely 
paralleled  among  the  very  "diverse  forms  shown  by  the  Kekchi  and 
other  primitive  Upland  types  that  have  been  introduced  from  tropical 
America  and  acclimatized  in  the  United  States  in  the  last  few  years. 

Several  of  these  newly  introduced  varieties  also  share  the  same 
characters  that  render  the  Hindi  variations  of  the  Egyptian  cotton 
so  strikingby  different  from  the  typical  Egyptian  plants,  such  as  the 

«  Local  Adjustment  of  Cotton  Varieties,     Bulletin  1">9,  Bureau  of  Plant  Industry, 
U.  S.  Dept.  of  Agriculture,  1909,  p.  17. 
[Cir.  53] 


MUTATIV]     1:1  VERSI0N8    IN    COTTON.  D 

Bhorter  lobes  of  the  leaves,  the  paler  preen  color,  and  the  thinner 
texture.  Two  <>r  three  of  the  calyx  lobes  of  the  Hindi  cotton  are 
usuall)  drawn  oul  into  a  long,  slender  tooth,  a  peculiarity  previously 
observed  onl)  among  the  Central  American  cottons.  Mr.  Rowland 
M.  Meade  has  found  thai  the  lobes  of  the  calyx  of  the  Hindi  cotton 
are  Bometimes  three-toothed,  as  also  occurs  in  the  Rubelzul  cotton, 
a  perennial  Upland  type  from  eastern  Guatemala  with  long,  pointed, 
Egyptian-like  bolls.  The  bolls  of  the  Hindi  cotton  have  a  rounded 
conic  form  and  are  abruptly  apiculate.  The  surface  is  Bmooth  ;i  m  I 
even,  with  the  oil  glands  deeply  buried  in  the  tissues,  another  tendency 
shared  with  several  of  the  Central  American  Upland  cotton 

The  agreement  of  the  Hindi  with  the  Central  American  types  of 
cotton  extends  even  to  the  frequent  display  of  two  types  of  foliage 

anions  unaccliinat  i/.ed    plants.      Both   types  yield   occasionally   la: 

luxuriant,  sterile,   or  late-maturing  plants   with  deeply   channeled 

ti\edohed  and  seven-lohed  leaves.  Smaller  and  more  fertile  plants 
have   the   leaves  more   nearly   plane,  with  only   the   usual   three   lobes 

regularly  developed.  Very  vigorous  Hindi-like  plant-  often  have 
the  same  general  appearance  as  Egyptian-Upland  hybrids  and  may 
represent   hybrids  between  the   Egyptian  cotton  and   the  extreme 

form  of  (he  Hindi.  The  large  si/.e  may  he  connected  with  the  fact 
that  characters  of  both  of  the  parent  types  are  brought  into  ex- 
pression. Nn  tendency  to  unusual  luxuriance  appears  in  Egyptian- 
Upland  hybrids  that  -how  the  characters  of  only  one  of  the  parent 
types.  The  unusual  vigor  appears  to  he  a  physiological  phenomenon 
in  some  way  connected  with  the  tension  or  conflict  in  the  expression 
of  the  divergent  characters  rather  than  a  consequence  of  sterility. 
The  abnormal  vegetative  vigor  l>c:_rins  to  he  manifested  in  the  earlier 
stages  of  growth,  before  any  of  the  plants  have  reached  bearing  age.* 

The  close  similarities  of  the  variant  forms  of  the  many  different 
kinds  of- cotton  may  be  taken  to  indicate  that  ancest  ral  charade  fist  ica 
are  returning  to  expression.  Otherwise  it  would  need  to  he  assumed 
that  the  many  diil'crent  kinds  of  cotton  are  engaged  in  the  formation 
of  closely  parallel  series  of  new  species.  Whether  the  cotton  varia- 
tions lx>  looked  upon  as  mutations  or  not,  it  is  equally  desirable  to 
recognise  their  relation  to  lever-ions.  It  might  he  as  proper  to  call 
them  revertive  mutations  as  mutative  reversions,  except  that  the 
idea  of  reversion  is  older  and  better  established  than  that  of  new 
species  or  new  character-  originating  by  mutation. 

The  range  of  ancest  ral  diversit  ies  that  may  he  expected  to  reappear 
in  reversions  must   be   learned  by  the  study  of  the  wild   relatives  of 

•  Origin  o!  the  Hindi  Cotton.    Circular  42,  Bureau  of  Plant  Industry,  U.  8    Dept. 
of  Agriculture      19 
►The  Vegetative  Vigor  of  Hyl>ri<ls  :ui<1  Mutations.     Proceedings,  Biological  Society 

<>t  Washington,  vol    i;.  vmw,  pp   v.  DO. 

(Cir.  53] 


6  MUTATIVE    REVERSIONS    IN    COTTON. 

our  domesticated  plants.  It  is  a  mistake  to  think  of  natural  species 
;is  uniform  groups  of  plants  that  show  only  one  set  of  characters, 
like  our  carefully  selected  varieties.  Very  few  of  our  cultivated 
plants  have  so  many  wild  or  unimproved  relatives  as  does  the  cotton, 
to  serve  as  a  basis  of  judgment  regarding  ancestral  diversities  and 
reversions. 

RELATION  OF  REVERSION  TO  COHERENCE  OF  CHARACTERS. 

Complete  reversions  may  be  considered  as  related  to  a  phenomenon 
already  described  as  coherence  of  characters.0  In  cotton  hybrids 
there  is  a  general  tendency  for  the  characters  derived  from  the  same 
ancestor  to  come  into  expression  in  groups  or  combinations.  It  sel- 
dom or  never  happens  that  a  single  character  of  one  ancestor  comes 
into  full  expression  in  a  hybrid;  that  is,  without  being  accompanied 
by  the  expression  of  other  characters  of  the  same  parent.  Coherence 
of  characters  appears  to  have  a  physiological  significance.  Among 
the  hybrid  plants  that  are  superior  to  the  parent  stocks  in  vigor,  fer- 
tility, and  quality  of  lint,  characters  of  both  of  the  parental  types  are 
brought  into  expression  in  coherent  groups.  Hybrids  that  bring  the 
characters  of  only  one  parent  to  full  expression  are  not  superior, 
while  those  that  show  incongruous  combinations  of  characters  are 
notably  deficient  in  fertility.  A  notable  example  of  this  relation 
appeared  in  a  field  of  Jannovitch  cotton  raised  from  imported  seed  at 
Somerton,  Ariz.,  in  1909.  The  plant  had  the  habit  of  growth,  leave-. 
and  bracts  of  the  Egyptian  cotton,  but  changed  suddenly  to  Hindi 
characters  in  the  long-toothed  calyx,  white  flowers,  and  broadly  conic 
light-green  bolls.  At  the  same  time  it  retained  the  Egyptian  charac- 
ters of  short  stamens  and  long  exserted  stigmas.  Though  having 
great  vegetative  vigor,  this  plant  was  quite  sterile.  The  anthers  con- 
tained pollen,  but  did  not  open  to  shed  it.  The  stigmas  were  abun- 
dantly cross-pollinated  by  insects,  but  no  ovules  developed  and  not 
a  single  boll  matured.6 

VARIATIONS  OF  DIVERSITY  IN  THE    SAME    STOCKS. 

The  fact  that  plants  with  a  preponderance  of  Egyptian  ancestn', 
such  as  three-quarters  or  upward,  may  show  little  or  no  sign  of  Upland 
admixture  accords  with  the  general  tendency  toward  coherence  in 

•^Suppressed  and  Intensified  Characters  in  Cotton  Hybrids.  Bulletin  147,  Bureau 
of  Plant  Industry,  U.  S.  Dept.  of  Agriculture,  1909,  p.  16. 

b  The  empty  carpels  of  this  plant  showed  a  further  peculiarity  not  hitherto  observed. 
The  ridge  that  marks  the  middle  of  the  wall  of  the  carpel,  the  line  of  dehiscence  of  the 
ripe  fruit,  gave  rise  to  a  series  of  long  slender  hairs  that  projected  into  the  cavitj  . 
Hairs  of  the  same  kind  were  found  afterwards  in  normal  plants  and  may  be  looked 
upon  as  an  additional  storm-proof  character,  since  they  undoubtedly  help  to  hold  the 
lint  and  seeds  in  place  after  the  carpels  have  opened. 
[Cir.  53J 


Mi    i  \  i  i\  i     REVERSIONS    IN  COTTON.  « 

the  expression  of  characters,  bul  coherence  alone  would  i><  >i  explain 
the  further  fad  thai  plants  of  preponderantly  Egyptian  ancestry 
may  depart  from  the  Egyptian  characteristics  and  appear  as  com- 
pletely un-Eg)  ptian  Upland  <>r  Hindi.  In  Btocks  where  the  crossing 
upon  tin'  Egyptian  is  limited  to  half-blood  Uplands  there  is  a  general 
reduction  of  the  expression  of  Upland  characteristics  as  compared 
with  iIh1  crosses  of  full-blood  Upland  upon  the  Egyptians,  bul  such 
dilutions  do  not  preclude  reversions  to  complete  Upland  forms. 

Upland  or  Hindi  characters  that  remain  completely  latent  or  without 
expression  in  one  generation  maj  recover  their  potency  and  return 
to  complete  expression  in  Borne  of  the  members  of  the  next  generation. 
One  planting  of  hybrid  seed  may  shoi*  a  preponderant  resemblance 
to  one  patent,  another  planting  to  the  oilier  parent.  One  planting 
of  a  stock  of  seed  may  show  none  of  the  Hindi  or  Upland  reversions, 
while  another  planting  of  the  same  stock  of  seed  or  another  part  of  the 
same  field  ma\  show  very  pronounced  examples.  Three  plantings 
of  the  Jannovitch  variety  of  Egyptian  cotton  in  1909  Bhowed  Hindi 
individuals  of  extreme  form,  although  a  large  planting  of  the  same 
stock  of  seed  in  L908  gave  only  a  lew  aberranl  individuals  in  which 
comparatively  slight  evidences  of  Hindi  contamination  were  detected." 

A  question  may  Mill  he  raised  regarding  the  authenticity  of  this 
extreme  example  where  complete  reversions  have  seemed  to  take 
place,  as  it  were,  by  wholesale.  Although  there  is  no  reason  to  doubt 
the  equality  and  genera]  uniformity  of  the  imported  Egyptian  seed, 

it  is  still  possible  to  imagine  that  the  seed  planted  in  1908  was  of  dif- 
ferent origin  from  that  grown  in  1909,  even  though  both  came  from 
the  s;mip  imported  stock.  Such  possibilities  :i^  the  sinking  of  the 
smooth  Hindi  seeds  to  the  hot  to  m  of  t  he  bag,  or  failure  to  germinate, 
or  early  death  of  the  Hindi  BeedlingS  have  also  to  he  reckoned  with, 
though  the  chances  that  BUch  accidents  could  afford  any  complete 
explanation  of  the  facts  appear  very  remote.  The  consistent  general 
behavior  of  the  Egyptian  plants  in  the  different  fields  and  experi- 
mental plats  and  the  general  scattering  of  the  Hindi  individuals  in 
the  plantings  of  1909  give  no  support  to  the  idea  that  the  Beed  was 
different.  An  absolute  determination  of  the  matter  will  require  the 
study  of  more  numerous  am!  -till  larger  plantings  of  Beed,  mixed  with 
special  thoroughness  t<>  avoid  the  possibility  of  accidental  segregat ion 
of  any  of  the  different  qualities  that  may  he  included. 

Regular  field  plantings  of  Egyptian  cotton  can  he  made  to  serve 

the  purposes  of  such  experiments,  but    it    is  desirable  to  present    in 

advance  the  collateral  evidence  for  expecting  that   reversions  will 

ur   and  that   they  tire    likely  to  appear  in  different   numbers  and 

■  A  Study  of  Diversity  in  Egyptian  Cotton  Bulletin  156,  Bureau  oi  Plant  Industry, 
i     -   Dept.  of  Agriculture,  1909,  pp   is--_>l. 

[Or.  S3] 


8  MUTATIVE    REVERSIONS    IX   COTTON. 

degrees  in  different  plantings,  even  when  the  seed  is  of  the  same  stock. 
Though  breeding  is  undoubtedly  a  very  important  factor  in  reducing 
diversity,  it  is  no  less  important  to  ascertain  the  relations  of  environ- 
ment to  the  occurrence  of  reversions.  Such  differences  of  behavior 
arc  frequently  shown  by  the  reversions  of  the  Upland  cotton,  and  the 
irregular  variations  of  the  Egyptian  cotton  appear  to  be  susceptible 
to  such  influences. 

Other  forms  of  reversions,  both  partial  and  complete,  have  shown 
relation  to  differences  of  environment  in  experiments  with  cotton. 
Ancestral  characters  that  are  prominent  in  one  locality  may  be 
entirely  suppressed  in  another  place  where  some  of  the  same  lot  of 
seed  has  been  planted.  Xot  only  the  amount  or  degree  of  reversion 
but  also  the  frequency  with  which  particular  characters  are  brought 
into  expression  is  subject  to  change  through  differences  of  external 
conditions.  The  failure  of  any  complete  Hindi  reversions  to  appear 
in  the  Jannovitch  planting  of  1908  does  not  appear  merely  arbitrary 
or  accidental  from  the  point  of  view  of  other  experiments,  but  nmy  be 
connected  with  the  facts  that  the  seed  was  sown  rather  late  and  that 
the  plants  developed  under  conditions  of  abundant  moisture  ami  heat 
that  have  shown  a  very  general  tendency  to  bring  the  extreme 
Egyptian  characters  into  expression.  Grown  under  such  conditions, 
plants  that  are  known  to  be  Upland  hybrids  usually  take  on  the 
complete  Egyptian  form  and  show  very  few  Upland  characters — 
sometimes  none  at  all." 

THE  HINDI  COTTON  CONSIDERED  AS  A  REVERSION. 

Young  plants  of  the  Egyptian  cotton  share  the  foliage  characters  of 
the  Hindi,  including  the  reddening  of  the  pulvinus,  the  wrinkled, 
swollen  cushion  where  the  veins  meet,  at  the  base  of  the  leaf.  If  the 
Egyptian  plants  are  kept  small  and  stunted  by  unfavorable  conditions 
the  resemblance  to  the  Hindi  continues  longer,  so  that  plants  that 
finally  develop  with  typical  Egyptian  characters  may  be  mistaken  for 
Hindi.  Late  in  the  season  there  is  another  partial  approximation 
of  the  foliage  characters,  for  the  Hindi  plants  generally  lose  the  red 
color  of  the  pulvinus  that  serves  as  one  of  the  most  conspicuous 
diagnostic  features  of  the  Hindi  at  earl}T  maturity  and  during  the 
preceding  stage  of  growth.  The  general  colors  of  the  leaves  are  also 
less  distinctive  in  the  latter  part  of  the  season,  the  Egyptian  cotton 
often  appearing  somewhat  lighter  and  some  of  the  Hindi  plants 
becoming  darker. 

Plants  that  do  not  show  very  distinct  Hindi  features  in  their  habits 
of  growth,  leaves,  bracts,  flowers,  or  bolls  may  still  betray  Hindi 

"  Suppressed  and  Intensified  Characters  in  Cotton  ITybrids.     Bulletin  147,  Bureau 
of  Plant  Industry,  U.  S.  Dept.  of  Agriculture,  1909,  pp.  17-23. 
[Clr.  53] 


\l  I    I  \  I  I  \  I     I 


9 


tendencies  in  their  naked  seed*  >rt,  sparse  linl       In  man}  bucIi 

,  g  the  petals  are  "l  a  somewhal  lighter  yellov  than  usual,  or  the 
purplespol  ma}  doI  be  w  deepl}  colored,  but  palei  petals  and  spo 
ma}  .»r. -in-  wnli. 'in  aii>  other  departure  I  I    jyptian  chai 

No  one  character  can  be  trusted  as  e\  idence  of  the  presei i  Hindi 

tendencies,  nor  is  their  an}  reason  to  suppose  thai  a  failure  to  sho* 
Hindi  characters  in  one  generation  excludes  their  appearance  in  an 
other,  any  more  than  withthesmall  boiled  andothei  inferior  reversions 
that  appear  in  Upland  varieties  Some  of  the  Hindi  charactei 
such  as  tin-  naked  black  Beed  with  short,  sparse  linl  confined  to  one 
.•ml.  air  a  feature  of  man}  small-boiled  reversions  thai  appear  in 
1 1  pi  and  col  ton. 

Instead  of  thinking  of  the  Hindi  cotton  as  a  distinct  independent 
type  which  has  become  hybridized  recently  with  the  Egyptian,  it 
ma}  be  considered  thai  the  Hindi  characters  merely  represenl  some 
of  the  extremes  of  variation  of  the  Egyptian.  Whether  the  two 
types  were  originally  distincl  or  nol  ma}  make  little  difference  with 
the  presenl  facts.  There  seems  to  be  no  definite  evidence  of  the 
independent  existence  of  the  Hindi  cotton,  either  as  an  indigenous 
wild  plant  or  as  a  domesl  icated  \  ariety.  It  would  doubtless  be  easy 
to  establish  the  Hindi  cotton  as  a  uniform  "pure"  stock  in  tin-  -am. • 
wax  thai  selection  can  establish  uniform  types  from  other  variati( 
of  the  Egyptian  cotton,  but  it  is  a  type  that  would  hardly  invite 
cultivation,    even    among  ~       \    pale-flowered    tree    cotton 

without  a  petal  spot  was  described  in  Egypt  by  Vesling  about  1640, 
and  Fletcher  is  inclined  to  believe  that  this  Was  the  prototype  of  the 
llmdi  cotton.  The  Egyptian  cotton  itself  is  supposed  to  have  hem 
brought  from  India  to  Egypl  only  about  a  centur}  ago,  bul  even  on 
this  reckoning  the  time  hascertainl}  been  ample  foi  themosl  complete 
intermixture  to  ha\  e  taken  pla< 

The  general  absence  of  intermediate  plants  ma}  be  taken  as  an 
indication  that  recenl  interbreeding  with  Hindi  has  been  avoided 
in  the  besl  of  the  imported  Egyptian  stocks,  bul  at  least  a  tew  ii 
viduals  of  the  extreme  Hindi  type  have  been  found  in  all.  The 
remarkabh  close  similarity  of  the  extreme  Hindi  plants  in  all  of  the 
newly  imported  stocks  also  supports  the  idea  that  such  plants  rep- 
resent complete  reversions.  It  is  ven  difficult  to  believe  that  all 
the  stocks  have  had  the  same  opportunities  of  securing  icent  inter- 
mixtures of  pure  Hindi  seed.  The  more  pronounced  of  the  Hindi 
plants  are  as  uniform  anion-  themselves  a-  the  Egyptian  plants  in 
the  same  stage  of  acclimatization.     Indeed,  they  appear  even  more 

tcher,  1        Thi  0  ir"i'1- 

vol   J.  m 

J7JH7      I  ir    53      L0 


10  MUTATIVE    REVERSIONS    IN    COTTON. 

uniform,  perhaps   as  a  result  of  the  strong  contrast  between  tnem 
and  the  norma]  Egyptian  plants. 

If  the  Hindi  plants  stood  alone,  they  would  be  identified  at  once 
as  members  of  a  series  of  Mexican  cottons  related  to  our  Upland  type, 
but  with  definite1  differences.  Some  of  the  varieties  contain  many 
plants  that  combine  the  Egyptian  with  the  Hindi  characters,  plants 
that  may  be  viewed  as  ordinary  hybrids,  hut  the  persistence  and 
remarkable  uniformity  of  the  Hindi  type  can  hardly  he  understood 
except  by  the  analogy  of  complete  reversions  to  the  Upland  type 
already  known  in  experiments  with  Egyptian-Upland  hybrids. 

CONTRASTED  CHARACTERS  OF  COTTON  REVERSIONS. 

Though  complete  reversion  may  not  have  been  formally  recognized 
as  a  phenomenon  of  heredity,  it  is  believed  that  an  examination  of 
related  facts  will  show  a  very  general  tendency  of  reversions  to 
extreme  expression  of  characters  rather  than  to  slight  or  intermediate 
expression.  Even  when  only  one  character  appeals  to  be  changed 
there  is  more  likely  to  be  a  complete  change  than  a  partial  one. 
Uniform,  deep-red  ears  are  a  much  more  frequent  reversion  in  corn 
than  ears  that  are  pale  red  or  that  have  only  a  part  of  the  kernels 
red.  Black  lambs  are  generally  black  all  over,  and  only  very  rarely 
spotted,  except  upon  the  head.  This  remains  true  even  when  black 
males  are  regularly  hied  with  white  females,  as  on  the  elevated 
plateaus  of  Guatemala,  where  the  Indians  prefer  the  black  wool. 
A  few-  piebald  sheep  were  finally  seen  in  one  flock,  but  only  after 
many  of  the  mixed  Hocks  had  been  looked  over  in  vain. 

Similarly  accentuated  contrasts  are  found  between  the  Egvptian 
cotton  and  the  Hindi.  The  veins  of  the  leaf  of  the  Hindi  cotton  are 
united  at  the  base  into  a  larger  and  more  prominent  cushion,  or 
pulvinus,  than  in  the  Egyptian  cotton,  and  the  pulvinus  of  the  Hindi 
cotton  is  rendered  the  more  conspicuous  by  its  red  color,  which  is 
shared  by  the  upper  side  of  the  somewhat  swollen  end  of  the  petiole, 
for  about  half  an  inch.  In  normal  Egyptian  cotton  the  pulvinus  is 
pale  green,  like  the  other  portions  of  the  veins,  or  only  slightly  tinged 
with  reddish,  like  the  end  of  the  petiole.  Under  some  conditions  the 
stalks  and  petioles  of  the  Egvptian  cotton  take  on  a  bright-red  color 
like  the  pulvinus  of  the  Hindi,  but  in  spite  of  the  reddening  of  most 
of  the  petiole  the  swollen  terminal  part  and  the  pulvinus  of  the 
Egyptian  leaf  remain  distinctly  paler.  Exactly  those  parts  that  are 
the  mosl  promptly  and  deeply  reddened  in  the  Hindi  plants  are  per- 
sistently paler  in  the  Egyptian. 

The  stalks  and  petioles  of  the  Hindi  plants  may  also  redden  with 
age,  as  in  the  Egyptian,  and  when  this  occurs  the  contrast  of  color 
is  destroyed,  for  the  red  of  the  pulvinus  and  the  swollen  end  of  the 

[bit  53J 


Ml  i  A  1 1 \  i.    i;i.\  BBSI0N8    IN    COTTON.  11 

petiole  fades  out,  bo  thai  these  parts  become  paler  than  the  remainder 

of  the  petiole,  as  in   the   red  stemi I  condition  of  the   Egyptian 

cotton      Bui  even  on  the  old  Hindi  plants  the  verj   young  lea 
whose  petioles  art  pale  have  the  pulvini  red. 

The  contrasl  is  aol  limited  to  the  color  alone,  i > ■  1 1  i^  carried  over 
into  the  hain  coverings  of  the  same  parts  The  lhn.li  cotton,  like 
the  Kekchi  and  other  Central  Aanerican  types  of  Upland  cotton,  lias 
the  pulvinus  and  the  adjacenl  reddened  pari  of  the  petiole  naked  or 
uiih  onlj  a  few  scattering  hairs,  even  when  the  real  of  the  petiole  is 
densely  hairy.  In  the  Egyptian  cotton,  on  the  contrary,  the  petiole 
generally  naked,  excepl  thai  hairs  arc  to  be  found  on  the  small 
pale  area  at  the  end  where  the  Hindi  cotton  i^  naked  and  red.  The 
pale-green  pulvinus  <>f  the  Egyptian  cotton  is  also  distinctly  hairy, 
especiallj  on  \  oung  lea^  es. 

A  similar  case  of  completely  conl  rasted  characters  has  1 n  brought 

to  m.\  attention  by  Mr.  G.  N.  Collins.  Some  of  the  Mexican  varieties 
of  coin  have  the  leaf  sheaths  almosl  complete!}  naked,  while  others 
have  them  almosl  completely  clothed  with  a  coal  of  line  hairs.  The 
contrast  is  strangely  accentuated  by  the  facl  thai  the  sheaths  thai 
are  otherwise  naked  have  a  oarrovs  hand  of  hairs  along  the  margins, 
while  the  marginal  hand  i->  naked  in  the  types  thai  have  the  hairy' 

sheaths. 

REVERSION  IMPLIES  CONTINUED  TRANSMISSION. 

The  facts  of  complete  reversion  have  a  practical  bearing  upon 
problems  of  breeding  and  acclimatization.  They  warn  us  not  to  rely 
upon  the  hope  of  being  able  to  effeel  a  complete  elimination  of  unde- 
sirable ancestral  characters,  in  the  sense  of  excluding  transmission. 
There  does  not  appear  to  be  any  direct  relation  between  the  visible 
expression  of  characters  in  a  plant  and  their  invisible  transmission  in  the 
germ  cells.  Characters  that  remain  latent  in  one  generation  may  lie- 
come  patent  in  another.  A  stock  that  appears  pure  under  one  gel  of 
conditions  may  appear  in  another  place  to  be  seriously  contaminated. 
The  latent  transmission  of  an  undesirable  character  does  no  harm 
as  long  as  the  latent  condition  continues,  but  the  return  of  such  a  char- 
acter to  expression  may  be  a  serious  injury  in  a  crop  like  t  he  Egypl  ian 
cotton,  where  the  uniformity  of  the  fiber  is  a  prime  requisite. 

Experiments  with  cotton  do  not  indicate  that  tendencies  to  rever- 
sion are  limited  to  particular  descendants  or  to  single  characters 
acting  independently,  as  sometimes  inferred  from  the  behavior  of 
Mendelian  hybrids.  Though  regular  Mendelian  relations  are  found  in 
cotton,  the  phenomena  of  heredity  are  evidently  nol  limited  to  the 
strictly  Mendelian   reactions   between   the  chi  "•indents  of 

Mendelism  usually  limit  then-  studies  to  reactions  between  varieties 

I   53] 


12  MUTATIVE    REVERSIONS    IX    COTTON. 

thai   have  been  brought  into  a  condition  of  uniform  expression  of 

characters,  but  other  kinds  of  reactions  are  not  less  interesting  and 
important.  The  uniformity  or  "  breeding  true"  of  a  few  generations 
of  individuals  docs  not  show  that  a  stock  is  "pure"«in  the  sense  em- 
ployed by  many  writers  on  Mendelism.  The  idea  that  the  Mendelian 
relations  of  expression  determine  the  "  presence"  or  "  absence  '  of  the 
characters  is  a  convenient  assumption  when  the  typical  Mendelian 
behavior  appears,  but  reversions  to  "latent"  characters  show  that 
expression  is  no  complete  index  of  transmission. 

The  idea  that  the  ancestry  of  our  cultivated  plants  is  to  be  traced 
hack  to  uniform  "pure"  stocks  that  transmitted  only  single  sets  of 
characters  finds  no  warrant  in  the  study  of  the  more  primitive  types 
and  wild  relatives  of  our  domesticated  species.  Diversity  of  expi 
sion,  instead  of  uniformity,  is  the  rule  in  nature,  and  the  transmission 
of  the  diverse  characteristics  does  not  cease  when  uniformity  of 
expression  is  enforced  through  selection.  Reversions  show  that  the 
underlying  inheritance  of  diversity  is  not  completely  lost,  nor  the 
power  of  the  ancestral  characters  to  reappear,  even  after  long  periods 
of  suppression. 

REVERSIONS  INTERFERE  WITH  MENDELIAN  EXPRESSION  OF 

CHARACTERS. 

The  tendency  to  reversion  has  to  he  reckoned  as  a  serious  obstacle 
to  the  utilization  of  hybrid  varieties  unless  the  external  conditions 
and  the  processes  of  reproduction  are  under  much  more  complete 
control  than  with  an  open-fertilized  field  crop. 

Mendel  pointed  out  a  very  useful  distinction  in  showing  that  two 
kinds  of  combinations  of  characters  are  represented  among  hybrids, 
some  stable  in  expression  and  others  unstable.  Intermediate  char- 
acters or  reversions  that  arise  from  divergent  tendencies  of  expression 
may  occur  with  much  regularity  in  the  first  generation  of  a  cross,  but 
may  afterwards  diminish  or  disappear.  Even  when  the  first  gener- 
ation shows  uniformly  intermediate  characters,  the  later  generations 
tend  to  revert  to  more  complete  expressions  of  the  parental  characti 
The  typical  Mendelian  relations  appear  in  crosses  between  strains 
that  differ  by  definite  tendencies  to  bring  certain  characters  to  full 
expression  or  to  leave  them  without  expression,  but  it  does  not  appear 
that  the  analogies  of  such  characters  are  applicable  to  all  kinds  of 
plants  or  to  all  classes  of  hybrids. 

Some  writers  on  Mendelism  have  supposed  that  inheritance  is 
governed  by  protoplasmic  determinants,  or  "units."  that  are  entirely 
separate  and  independent,  so  that  some  of  them  can  be  changed  with- 
out disturbing  the  others,  like  changing  the  letters  of  a  word  or  the 
words  of  a  sentence.      Individual  words  from  related  languages  can 

[Cir.  53] 


Ml    I  \  I  l\  I     1:1  \  i  KSION8    in    COTTON. 

often  be  combined  into  a  hybrid  sentence  withoul   disturbing  the 
general  grammatical  Btructure,  much  .1-      nun   characters     app< 
to  be  substituted  for  each  other  in  strictly    Mendelian  hybritls.     In 
other  cases  the  words  of  two  languages  <li>  not   prove  t"  be  direct 
equivalents,  bul  require  differenl  grammatical  relations.     Sentero 
can  ito  longer  be  translated  piecemeal,  by  individual  words,  l>ui  have 
to  be  recast  by  whole  phrases  i>r  clauses.     Words  derived  from  the 
same  language  tend  to  keep  together  in  the  hybrid  sentence,  in  the 
Minic  way  that  characters  of  diverse  parental  types  hold  together  in 
expression.     1 1\  brids  that  gave  intermediate  or  combined  expression 
of  Egyptian  and  Upland  characters  in  the  earl}   generations  have 
shown   a   distinct    tendency    toward    more   exclusive   expression 
Upland  characters  in  later  generations,  even  when  selected  for  the 
expression  of  Egyptian  or  intermediate  characters. 

[f  ilic  existence  of  determinant  particles  or  character  units  is  to  be 
assumed,  it  is  more  reasonable  to  suppose  that  the  expression  of  the 
characters  is  governed  by  positional  relations  among  the  particles 
than  by  mere  presence  ot  absence  of  particles.  The  theory  of  posi- 
tional relations  of  determinants  was  suggested  by  Mr.  Walter  T 
Swingle, of  this  Department."  It  has  the  advantage  of  accommodat- 
ing a  wider  range  of  facts  than  the  Mendelian  theory  .  The  establish- 
ment of  definite  position-  among  the  particles  would  account  for  con- 
ditions of  uniformity  and  for  regular  Mendelian  ratios  of  expression, 
while  mutative  reversions  and  diversified  hybrids  can  be  ascribed  to 
disturbances  of  the  positional  relations.  Thus  the  positional  theon 
admits  the  transmission  of  latent  characters  as  a  general  condition  of 

inheritance,  whereas  Mendelian  writers  have  treated  laten<\  as  an 
exceptional  phenomenon  requiring  to  be  explained  by  additional 
theories. 

Mendelian  combinations  of  characters  do  not  promise  to  attain 
great  importance  in  cotton  because  of  the  general  tendencies  to  rever- 
sions and  correlations  of  characters  that  interfere  with  stable  combi- 
nations between  characters  derived  from  different  types.  Reversions 
transgress  the  Mendelian  program.  They  interfere  with  Men- 
delian dominance  in  the  firs!  generation  and  with  Mendelian  combi- 
nations and  segregations  of  characters  in  the  later  generations.  A 
Mendelian  combination  of  the  naked  seeds  of  one  variety  with  the 
abundant  lint  of  another  mighl  be  desirable,  but  naked-seeded  hybrids 
are  prone  to  revert  to  sparse  lint,  so  that  the  yield  is  not  likely  to  l>e 
maintained.  Fuzzy-seeded  types  are  preferred  because  of  the  greater 
abundance  of  lint. 


"  I11  a  paper  read  at  a  meeting  <>f  the  Society  Cor  Plant  Morphology  and  Phyi 
entitled  "Some  Theories  ol  Heredity  and  of  the  <  Origin  of  Species  •  onsidered  in  B 
tion  to  the  Phenomenon  ol  Hybridisation."     Abstract  published  in  the  Botai 
c.    vol,   25,   do.    111.    '• 

[Cir 


14  .MUTATIVE   REVERSIONS   IN    COTTON. 

REVERSIONS  OF  LATER  GENERATIONS  OF  HYBRIDS. 

Many  attempts  have  been  made  to  obtain  early  and  prolific  Egyp- 
tian or  Sea  Island  varieties  by  crossing  with  Upland,  and  the  first 
generations  of"  such  crosses  often  appear  very  promising.  The  diffi- 
culty  is  that  the  later  generations  not  only  revert  to  the  parental 
types,  but  often  go  farther  hack,  to  the  condition  of  remote  unim- 
proved ancestors.  Instead  of  having  longer  lint  than  the  Egyptian 
parent,  as  the  first  generation  usually  does,  the  later  generations 
become  inferior  even  to  the  Upland  parent.  Hybrids  representing 
the  fourth  and  fifth  generations,  grown  at  San  Antonio.  Tex.-,  in  the 
season  of  1909,  did  not  show  a  single  plant  with  good  Egyptian  lint, 
and  very  few  that  were  better  than  ordinary  Upland.  This  extreme 
deterioration  might  he  ascribed  partly  to  adverse  conditions,  hut  first- 
generation  hybrids  grown  under  the  same  conditions  produced  excel- 
lent lint,  longer  and  stronger  than  the  Egyptian  parent.  These  con- 
trasts between  the  different  generations  show  that  the  hybrids  do 
not  merely  fail  to  fix  particular  combinations  of  the  parental  charac- 
ters, hut  may  first  exceed  the  parents  and  then  suffer  serious  deteriora- 
tion. The  characters  of  the  lint  that  have  received  the  most  selec- 
tion show  the  most  striking  deterioration.  Such  hybrids  promise  to 
have  practical  value  only  in  the  first  generations.  The  prohlem  of 
utilization  turns  upon  the  possibility  of  raising  commercial  quantities 
of  hybrid  seed." 

The  fact  that  hybrids  of  later  generations  often  show  characters 
different  from  those  of  the  first  generation  has  been  taken  as  proof 
of  the  Mendelian  theory  of  separate  transmission  of  contrasted  char- 
acters. Characters  that  appear  in  all  of  the  individuals  of  the  first 
generation  but  not  in  all  of  the  second  or  later  generations  have  been 
ascribed  to  the  presence  of  two  independent  Mendelian  "factors'" 
that  are  supposed  to  be  transmitted  separately,  and  not  recombined 
in  all  the  members  of  the  later  generations,  but  in  only  half  of  them. 

This  theory  would  explain  why  half  of  the  second  generation  might 
fail  to  show  a.  character  that  appeared  in  all  of  the  first  generation, 
but  it  gives  us  no  suggestion  of  the  complete  disappearance  of  the 
long  lint  in  the  later  generations  of  the  cotton  hybrids.  There  is  no 
reason  to  suppose  that  the  internal  '"factors"  that  produce  the  long 
lint  in  the  first  generation  of  a  hybrid  cease  to  be  transmitted  to  the 
later  generations,  but  there  are  serious  differences  in  the  external 
expression  of  the  characters.  Factors  that  influence  the  expression 
of  characters  have  to  be  considered,  not  merely  the  possibilities  of 
alternative  transmission.     A  character  that   has  been  expressed   in 

a  Suppressed  and  Intensified  characters  in  Cotton  Hybrids.     Bulletin  147,  Bureau 
of  Plant  Industry,  1".  S.  Dept.  of  Agriculture,  1909,  p.  15. 
[Clr.  53] 


Mi    ;  \  i  i\  i.    REV]  RBI0N8    IN  COTTON.  L5 

intensified  form  in  the  firsi  generation  maj  I"-  reduced  or  suppressed 
in  later  general  ions. 

It  mux  be  thai  more  strictl)  Mendelian  reactions  might  have  been 
secured  if  the  experiments  had  been  preceded  bj  courses  "I  Btricf 
line  breeding,  as  in  many  Mendelian  investigations,  bul  this  would 
not  insure  results  of  practical  value,  because  there  is  no  waj  to  enforce 
the  Mendelian  condition  of  Belf-fertilization  in  field  cultures  of  cotton. 
It  is  also  possible  that  a  course  of  self-fertilization  would  have  the 

effecl  of  more  definitely  fixing  the  expressi f  the  desirable  charac 

ters,  and  render  the  later  generations  less  liable  to  shoM  variations 
and  reversions.  These  questions  are  worthj  of  careful  investigation, 
though  such  physiological  effects  of  line  breeding  upon  expression 
are  DOl    taken   into  account    in   the  Mendelian  doctrine  of  pure  germ 

cells. 

Uniformity  is  much  greater  and  more  easily  maintained  among 
the  descendants  of  an  individual  mutation  than  in  a  hybrid  stock. 
From  the  breeding  standpoint  this  greater  tendency  to  uniformitj 
ma\  be  reckoned  as  the  chief  difference  between  the  reversions  that 

OCCUr  as  mutation-,  and   those  that    are   found   among  hybrids.      The 

range  of  variation  among  the  mutations  appears  to  be  as  great  as 
among  the  hybrids,  and  warrants  the  expectation  thai  almost  any 
desirable  combination   of  characters   may   be   found   by   persistent 

search. 

The  apparent  tendency  of  mutative  reversions  to  come  true  from 
seed  suggests  another  possibility  of  making  combinations  of  charac- 
ters between  diverse  type-  n  hose  hybrids  fail  to  show  definite  Mende- 
lian reaction-.  Instead  of  attempting  to  establish  immediate  unions 
between  the  character-  of  such  species  as  the  Egyptian  and  Upland 
cottons,  attention  may  be  given  to  the  occasional  mutative  reversio 
that  appeal-  in  dilute  hybrid  stocks.  Such  mutation-,  mighl  nol  have 
the  special  vigor  and  fertility  of  first-generation  hybrids,  hut  they 
might  yield  more  uniform  progeny.  A  stock  of  Egyptian  cotton  that 
had  once  been  hybridized  \\ ith  Upland  mighl  furnish  a  series  of  muta- 
tive variations  more  promising  for  breeding  purposes  than  a  stock  ol 
diverse  hybrids.  The  application  of  this  method  involves  the  diffi- 
culty of  producing  and  giving  careful  study  to  the  large  number  ol 
reversions  that  might  need  to  he  inspected  before  a  particular  com- 
bination <>f  characters  could  be  found.  Most  of  the  reversions  will  be 
inferior,  hut  an  occasional  superior  type  ma\  he  expected.  Even 
among  the  Hindi-like  variations  of  the  Egyptian  cotton  there  are 
some  that  are  above  the  average  of  the  Egyptian,  in  Bpite  of  the 
extreme  inferiority  of  the  lint  characters  of  the  extreme  Hindi  type. 
[dr.  53] 


16  Ml    DATIVE    REVERSIONS    IN    COTTON. 

AGRICULTURAL  SIGNIFICANCE  OF  REVERSIONS. 

II'  the  Hindi  characteristics  continue  to  reassert  themselves  in  the 
Egyptian  cotton,  complete  reversion  is  a  less  serious  obstacle  to  com- 
mercial uniformity  than  partial  reversion.  Jt  is  much  easier  to  recog- 
nize and  destroy  the  complete  Hindi  plants  than  the  intermediate 
individuals  that  give  only  slight  expressions  of  the  Hindi  character- 
istics. 

In  plantings  of  the  superior  Jannovitch  and  Nubari  varieties  the 
proportion  of  the  complete  Hindi  reversions  has  exceeded  that  of  the 
plants  that  show  an  intermediate  or  partial  expression  of  the  Hindi 
characters.  This  is  in  notable  contrast  with  the  behavior  of  a  planting 
of  the  older  and  less  improved  Ashmuni  variety,  where  a  large  pro- 
portion of  the  plants  show  some  of  the  Hindi  characters.  Whether 
these  differences  should  be  ascribed  to  the  more  careful  breeding  of 
the  Jannovitch  and  Nubari  varieties  or  to  the  different  conditions  of 
the  fields  is  not  certain.  It  may  be  that  the  intermediate  plants 
represent  new  or  relatively  recent  crosses  between  the  Hindi  and 
Egyptian  forms  of  plants,  rather  than  partial  reversions,  but  the 
large  numbers  of  plants  that  show  Hindi  seed  characters  indicate  a 
very  general  presence  of  Hindi  tendencies,  at  least  in  the  Ashmuni 
stock.  In  any  case,  the  recognition  of  the  complete  reversions  will 
assist  the  careful  planter  in  learning  to  detect  the  Hindi  characteris- 
tics, even  in  their  less  conspicuous  degrees  of  expression. 

Hybrids  and  extreme  forms  of  reversions  are  not  the  only  types  of 
deterioration  that  must  be  guarded  against  if  the  need  of  a  high  degree 
of  uniformity  is  to  be  met.  Many  plants  that  do  not  depart  from  the 
Egyptian  characteristics  will  be  found  to  fall  far  below  the  standards 
of  an  improved  variety,  either  in  fertility  or  in  the  qualities  of  the 
lint.  There  is  no  reason  to  suppose  that  uniformity  can  be  main- 
tained without  continued  selection  in  any  field  crop  grown  from  seed.0 

If  reversions  were  to  be  looked  upon  as  ordinary  hybrids  like  those 
that  result  from  recent  crossing,  it  would  appear  impracticable  to 
guard  the  crop  from  contamination,  and  hence  impossible  to  obtain  a 
uniform  commercial  product.  No  matter  how  carefully  the  fields  of 
the  Egyptian  cotton  may  be  isolated,  variations  may  still  occur  that 
can  easily  be  mistaken  for  hybrids.  The  difficulty  of  securing  ade- 
quate isolation  of  the  Egyptian  cotton  will  be  serious  enough  in  any 
regions  where  Upland  cotton  is  grown,  but  it  need  not  be  exaggerated 
by  the  condemnation  of  stocks  that  may  continue  to  show  reversions 
without  recent  contamination. 

The  occurrence  of  reversions  in  one  locality  or  in  one  season  need 
not  stand  in  the  way  of  early  return  to  practical  uniformity  if  an 

"Local  Adjustment  of  Cotton  Varieties.     Bulletin  159    Bureau  of  Plant  Industry. 
U.  S.  Dept.  of  Agriculture,  1909,  pp.  56-62. 

[C'ir.  53] 


Ml    I  A  I  l\  I     K!  \  I  RSI0N8    I.N    I  <>|  l".\.  1  7 

adequate  selection  is  maintained  and  favorable  conditions  air  pro 
Tided.     Familiarity  with  the  vegetative  characters  « « f  the  plants  \nll 
enable  the  undesirable  reversions  to  be  rogued  out  before  tin-  time  of 
flowering,  so  that  crossing  with  such  plants  ma)  be  avoided.     Tend 
encies  to  variation  that  are  shown  in  the  lint  and  the  seeds  can  be 
rejected  when  the  necessary  selections  are  made  in  the  fall  to  sei 
high-grade  seed  for  tin*  next  season's  planting.     The  influence  of  the 
external  conditions  upon  reversions  is  onl)  one  "f  many  indications 
thai  the  uniformit)  of  the  crop,  as  well  as  the  yield  of  fiber,  will  dc 
pend  upon  cultural  methods  as  well  a>  upon  the  Beed  that  i-  planted. 

CONCLUSIONS. 

The  phenomenaof  reversion  in  cotton  are  n<>i  confined  to  the  changes 
of  single  characters,  hut  ma)  result  in  wide  departures  from  parental 
types  and  bring  different  series  of  \  ariet  al  characters  into  expression. 

Tin'  return  of  ancestral  characters  to  expression  does  ool  depend 
upon  recent  hybridization,  l>ut  ma)  be  shown  in  abrupt,  mutative 
variations  of  "pure-bred"  stocks  that  have  been  selected  for  the  uni- 
form expression  of  a  Bingle  set  of  characters. 

Reversions  may  be  aroused  b)  new  or  unfavorable  conditions  ol 
environment  and  may  vary  in  extent  and  frequency  with  changes  of 
external  conditions.  The  uniformity  of  a  stock  in  one  place  affords 
no  assurance  that  diversity  will  not  reappear  in  another  locality. 
Diverse  characteristics  continue  to  be  transmitted  and  may  return 
to  expression  after  many  generations. 

The  variations  of  the  different  types  of  cotton  have  general  simi- 
larities  and  may  be  arranged  in  parallel  series.  The  general  range 
of  the  ancestral  diversities  of  cotton  is  also  to  be  learned  .from  the 
study  of  wild  or  unimproved  types  and  from  the  diversities  that  in- 
terfere with  t  lit*  Mendelian  expression  of  characters  in  hybrids. 

The  uniformity  <>f  the  progeny  of  mutative  variations  renders  them 
greatly  superior  t«>  hybrids  for  breeding  purposes.  The  possibility 
of  obtaining  superior  mutative  reversions  from  later  generations  of 
dilute  hybrid  stocks  is  worthy  of  investigation,  especially  in  cases 
where  desirable  Mendelian  combinations  are  not  obtained  in  the  earlier 
general  ions  of  hybrids. 

The  Hindi  \  ariat  ions  of  t  he  Egypt  ian  are  similar  in  their  characters 
and  behavior  to  some  of  the  reversions  that  appear  in  Upland  varie- 
ties and  may  prove  to  he  forms  of  reversion  rather  than  result-  of 
recent  contamination  with  a  distinct   type  of  cotton. 

The  more  pronounced  form-  of  reversion  in  Upland  cotton,  like  the 
Hindi  variations  of  the  Egyptian  cotton,  are  readily  distinguished  by 
Vegetative  character-,  so  that  they  can  he  rogued  out  before  the  time 
[dr.  53] 


18  MUTATIVE    REVERSIONS    IX    COTTON. 

of  ilowering,  to  avoid  the  contamination  of  the  stock  by  cross- 
pollination. 

Partial  expressions  of  Hindi  and  other  inferior  characters  can  often 
be  detected  in  the  lint  and  seed,  even  when  not  shown  in  the  vegeta- 
tive characters  of  the  plants.  Such  tendencies  are  to  be  taken  into 
account  in  the  annual  selection  of  seed. 

It  is  also  of  practical  importance  to  distinguish  between  the  Hindi 
variations  of  the  Egyptian  cotton  and  the  variations  that  result  from 
crossing  with  Upland  cotton.  If  reversions  are  mistaken  for  results 
of  recent  hybridization  it  may  appear  impossible  to  guard  the  Egyp- 
tian or  other  superior  types  of  cotton  from  Upland  contamination, 
though  there  is  every  reason  to  believe  that  distances  of  a  few  miles 
will  afford  complete  isolation. 

Approved: 

James  Wilson, 

Secretary  of  Agriculture. 

Washington,  D.  C,  February  2,  1910. 

[Cir.  53] 

O 


UNIVERSITY  OF  FLORIDA 


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